HOW TO KNOW THE SEAWEEDS 



35a Thallus showing a single axial filament of very large cells cov- 

 ered by a thin cortex of much smaller cells. Fig. 57 36 



Fig. 57. Ceramium sp. 



A longitudinal section through a node to 

 show two of the large central axial cells and 

 the thin cortex of small cells covering them, 

 X 65. This structural feature usually may be 

 discerned by obtaining a median optical focus 

 with the microscope using strong light. 



Figure 57 



35b Axial filament not as above; if present, borne within a medullary 

 tissue. Fig. 58 38 



Fig. 58. Endocladia muiicata (Postels & Ruprecht) 

 J. Agardh 



A cross section of a branch to show the con- 

 spicuous large axial filament and the radiating 

 medullary filaments, X 50. 



Figure 58 



38a Cortical cells in regular vertical rows; axes bearing whorls of 2- 

 celled spines at regular intervals. Fig. 59. .Centroceras clavulatuzn 



Fig. 59. Centroceras clavulatum (C. Agardh) Montagne 



A small part of a branch to show the regular ar- 

 rangement of the cortical cells and the whorls of 

 spines X 120. A common small plant of Florida, 

 the Gulf of Mexico and southern California, often 

 mixed with other small algae in tufts. 



Figure 59 



56 



